As the communication technology has developed towards personal, mobile, and broadband directions, the mobile technique, wireless technique, broadband technique, and multimedia communication technique have become critical techniques for research. In addition to the establishment and convergence of a core network, an access network is one of the bottlenecks restricting the network performance. Therefore, a broadband wireless access (BWA) technique is one of the key techniques for the development of the next generation communication networks. The access techniques may be divided into various categories according to a wired type and a wireless type, or a fixed type and a mobile type.
It is well known that, the higher the frequency is, the quicker the attenuation of the radio waves is with the changing of the distance. A high working frequency results in a quite limited coverage of a base station. Thus, by adding wireless relay stations in the network, the coverage of the system can be enlarged or the throughput of the system can be improved.
The wireless relay station communicates with the base station via an air interface, and forwards a data from a terminal. The most advantageous feature of the wireless relay station lies in that it does not need cables when being connected to the core network, so that the laying operation thereof is more flexible than that of the base station in the conventional art. Therefore, under the same system performance requirements including the coverage and throughput of the system, the cost for establishing a relay station is lower than that for establishing a base station. Thanks to the above advantageous characteristics, the relay station may be quickly laid, and the operation cost is relatively low. Therefore, by using the relay station, a larger coverage can be achieved with lower cost, and thus, the market demands for the wireless broadband access network may be increased accordingly.
Recently, a random access process of a mobile terminal is an indispensable process before mobile terminals in all the communication systems get access to the network, the random access process mainly occurs in two situations as follows. The first situation is after the mobile terminal is booted and before the connection with the network is established, and the second situation is after the mobile terminal receives a paging from the network and before the connection with the network is established once again from an idle state. However, during the process of implementing the present invention, the inventor(s) finds that, in both the above situations, the mobile terminal needs be located within the coverage of the base station, so as to implement the random access process. That is to say, if the mobile terminal is not located within the coverage of the base station, even if the mobile terminal is located within the coverage of relay stations, the random access process still cannot be implemented.
In addition to the mobile terminal, the new access node may be a newly-access relay station. Therefore, if the relay station is not within the coverage of the base station, even if the relay station is located within the coverage of other accessed relay stations, the random access process thereof still cannot be implemented.